1. Field of the Invention
The present invention relates to an active matrix display device in which pixels arranged in a matrix and driving circuits disposed peripheral thereto are formed so as to be incorporated, and in particular to the structure of such a peripheral circuit.
2. Description of the Related Art
By referring to FIG. 6, an example of a conventional active matrix display device will be briefly described.
The display device has pixels LC arranged in a matrix as shown in the figure. The respective pixels include pixel electrodes formed on one substrate and counter electrodes formed on another substrate, with an electro-optical material such as liquid crystal provided therebetween. A predetermined voltage V.sub.com is applied to the counter electrodes. The respective pixels LC are connected in parallel to additional capacitors Cs. In addition, thin film transistors Tr are formed so as to be integrated, as switching devices for driving the respective pixels LC. Gate lines X are arranged along the row direction of the pixels LC arranged in a matrix, while data lines Y are arranged along the column direction perpendicular thereto. The source electrodes of the thin film transistors are connected to the corresponding data lines Y, while the gate electrodes are connected to the corresponding gate lines X.
The display device further includes a vertical driving circuit 101 and a horizontal driving circuit 102. The vertical driving circuit 101 sequentially outputs selection pulses to the gate lines X, enabling the thin film transistors Tr on the same gate line to be conductive, and performs line-sequential-scanning of the pixels LC in line units. The vertical driving circuit 101 sequentially transfers a vertical start signal VST that is inputted from an external timing generator, in synchronism with a vertical clock signal VCK which is similarly inputted from the timing generator, and thereby outputs the above-mentioned selection pulses. Also, the horizontal driving circuit 102 controls switching of switches HSW connected to the respective data lines Y. The data line Y are supplied with a video signal SIG that is separated into three primary color components of red, green and blue. In synchronism with a horizontal clock signal HCK inputted from the external timing generator, the horizontal driving circuit 102 outputs selection pulses, which control switching of the switches HSW, by sequentially transferring a horizontal start signal HST similarly inputted from the timing generator in one horizontal period. Thereby, the video signal is written into the pixels LC in the row selected in each horizontal period.
FIG. 7 shows a block diagram of an example of the detailed structure of the horizontal driving circuit 102. The vertical driving circuit 101 also has a similar structure. The horizontal driving circuit 102 outputs the selection pulses .phi. for sequentially switching the switches HSW shown in FIG. 6. The horizontal driving circuit 102 consists of D-type flip-flops (D-F/F) connected in series in multistages which correspond to the number of the pixel columns. When receiving the clock signal HCK, the horizontal driving circuit 102 sequentially transfers the start signals HST, and thereby outputs the selection pulses .phi..
Also in active matrix display devices having a screen consisting of matrix-arranged pixels and peripheral driving circuits, the screen has been being developed for larger size and higher resolution. This case increases the number of connected D-F/F which are included in a shift register which constitutes a driving circuit. As shown in FIG. 7, if a defect occurs in part of the D-F/Fs connected in series or at a connection, the horizontal start signal HST is not transferred after where the defect occurs, and selection pulses are not outputted in the remaining stages. Consequently, video signals cannot be written into the portions of the screen corresponding to the remaining stages, which thus causes a fatal inferior display. In addition, according to the conventional driving circuit using the shift register, the sequence of the selection pulses outputted becomes uniform, which makes it difficult to perform various displays with respect to the screen.